95 SILVERADO LOPE

This is a 95 350 2wl drive Sil. Between the 1000 and 2000 rpm range, the truck shudders hard from idle to load. I have replaced every ignition and charging component except the ignition module which checked out fine. Plugs, plug wires, alt, battery, coil, etc... I've talked to GM, the dealerships, Chevy experts online, and in person without any success. One local mechanic suggested that these models developed a worn bearing on the distributor that seemed to explain the lope and I replaced that without any joy. I've heard that this isn't an isolated problem, but no one can remember how they fixed it when asked. Or who it was that did it. It's been over two years and I've grown to just deal with it. I'm still waiting for that traffic stop for erratic driving happen.

pull the distributer cap and the rotor.. take a bright flash light and look at the second layer of the distributer reluctor.. for cracked a magnet..

what happens is because of the electronic spark control.. the ignition coil is not triggered on the pulse but on the next pulse using a count down to control the timing advance.. these cracks create ghost patterns that trigger out of phase random count downs that cause horrible and ODD misfiring, stumbling issues...

this is what a V6 distributer looks like with a reman aftermarket pickup and reluctor.. far superior design..

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next.. while you are in the engine compartment..

engine off.. grab the throttle lever on the side of the throttle body... open the throttle slightly... see if the shaft wiggles in the bore... (O) good.. .,,,, (O ) ( O) bad.. what happens the throttle shaft closes to a different angle each time.. this can cause issues with drivability.. both idling and during acceleration.. as the throttle is opening part way.. but not changing the angle just slightly after the throttle starts to open.. this effects the throttle position sensor voltage.. some carb shops can rebush the throttle body.. some mechanics can also. i do it with a few specialized tools and 0.375 Kline valve guide liners and a letter Y drill. and a .375 valve guide reamer.. not stuff found in regular tool boxes.. the screws that hold the blades on the shaft are TINY and have to have the exposed threads ground off before removal is attempted.

i took a series of pictures of how i rebush them but screwed up with my previous cell phone camera.. overwrote them all..

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while up on top of the engine .. please use a mirror and flashlight or just a flashlight to read the part numbers off the top of the injectors.. or look at the colors of the insulation pins that stick up.. could you have incorrect fuel injectors??? 305 injectors or 4.3 injectors in a 5.7 or larger motor creates a HORRIBLE flat spot coming off idle... when the system reverts to open loop and runs on preprogrammed fuel injection values.. it will be too lean ..

because you have a 1995 model.. its very hard to get codes out without a proper OBD1.5 scan tool.. or even look at the live data stream .. thats one place you need to examine..

i have more stuff.. but please check these.. post in detail what you find....

i am very familiar with these TBI systems and trouble shooting them...

if you have an OBD1 or OBD1.5 scan tool... some 95 models came with an OBD2 16 pin connector under the dash.. verses the 12 pin obd1 gm connector..

take a look at the connector...

if you have the OBD2 connector.. you might be able to use the harbor freight 98614 OBD2 scan tool to access the system.. get the lines of data and type post them while the engine is cold engine off, key on..... fully warmed up engine idling... and at 2500 RPMS fully warmed up..

print this chart out.. copy the data for every line onto it.. post those numbers ...

i can usually tell an issue from there.. these are generic values.. and are somewhat misleading..